The invention relates to a cathodic system having a planar target for vacuum sputtering systems for the application of dielectric or nonmagnetic coatings to substrates, and having a magnetic field generator disposed behind the target as seen from the substrates, and insulated from the target.
In contrast to the vacuum depositing method, the rate of deposition, i.e., the amount of coating material deposited per unit of time, is relatively low in the cathodic sputtering process. Consequently a number of methods have become known for the purpose of increasing the rate of deposition of the coating material. This can be accomplished, for example, by raising the temperature level of the cathode or target, by increasing the pressure prevailing in the apparatus, by the production of magnetic fields, and/or by the production of high-frequency discharges within the sputtering depositing apparatus. A high rate of deposition is in many cases essential to economically feasible production.
Through German Pat. No. 737,613 it is known to increase the rate of deposition, when a cathode in the form of a planar coil is used, by raising the cathode to a higher temperature level by direct current flow. In this case, however a thermal stress is unavoidably applied to the substrates, which in many cases is undesirable. A magnetic field, which of itself would also tend to increase the rate of deposition, is said to be prevented by supplying the cathode with alternating current as the heating current and with a pulsating direct current of the same frequency with a certain phasing.
From German Offenlegungsschrift 15 15 296, it is known to increase the atomization rate by making a planar coil of the material to be deposited, for example, and supplying it with high-frequency current. Such a method, however, is limited to the production of coatings of an electrically conductive material. Furthermore, even so, the rate of deposition is not increased in a desirable manner.
Through German Offenlegungsschrift 16 90 691 in conjunction with German Pat. No. 15 15 313, it is furthermore known to dispose a plurality of rod-shaped individual cathodes parallel to one another in one plane and to bring them alternately to different alternating current potentials, while a direct or alternating current flows simultaneously through the individual rods producing a magnetic field which increases the ionization probability. Such an apparatus, however, necessitates a galvanic separation of the individual cathode rods, involving a large number of voltage and current lead-throughs as well as separate power supplies for feeding current to the cathode rods for the production of the magnetic field. If such an apparatus is to be used for the spray application of dielectric coatings, the only possibility is to cover the individual cathode rods with tubes of the dielectric material. The desirable uniformity of the deposited coatings cannot be achieved in this manner.
Through U.S. Pat. No. 3,878,085 it is furthermore known to dispose, on the side of the target material facing away from the substrates, an oval or circular pole shoe system which produces a magnetic field whose lines of force pass out through the target surface and, after describing arcuate paths, return into same. In this manner it is possible to obtain a desirably high atomizing and depositing rate. The uniformity of the coating density distribution is also satisfactory as long as the substrates are within an area which is markedly smaller than the target area. An important disadvantage in this case, however, is that the rate of atomization of the target material varies greatly according to the local field strength, so that during the atomization, deep grooves form in the target corresponding to the shape of the magnetic field. For this reason only about 30% of the expensive target material can be utilized.
Lastly, it is also known to equalize the atomization rates, which differ greatly from one area to the next when a magnetic field is used, by keeping the magnetic system in constant movement relative to the target material. Aside from the fact that this requires a complex mechanical system, the utilization of the target material cannot be greatly improved, i.e., it cannot be increased much beyond about 50 to 60%.